Abstract 5956: New molecular mechanisms of small cell lung cancer growth

Lung cancer is the leading cause of cancer death among both men and women in the United States. Small cell lung cancer (SCLC) results in over 30,000 deaths of Americans annually and comprises 15-17% incidences of lung cancer. SCLC is the most aggressive form of lung cancer due to its rapid doubling time and early widespread metastasis. Most SCLC patients present with advanced disease, respond to initial systemic chemotherapy, and then treatment refractory progression usually occurs within one year due to acquired drug resistance. Consequently, the median survival time of SCLC patients is only 9 to 20 months and merely 7% of SCLC patients survive beyond five years. A better molecular understanding of SCLC is necessary to develop much needed new treatment strategies. For the first time, we demonstrate that dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32) and its splice variant t-DARPP stimulate tumors of neuroendocrine origin, and we show DARPP-32 proteins are aberrantly overexpressed in human SCLC. Upregulation of t-DARPP protein in a subset of SCLC patients positively correlates with overexpression of genes associated with Notch signaling, including achaete-scute homologue 1 (ASCL1). We reveal that DARPP-32 isoforms are transcriptionally activated by ASCL1 in human SCLC cells. To determine whether DARPP-32 drives SCLC growth in vivo, we utilized an orthotopic lung cancer xenograft mouse model. Mice challenged with DARPP-32-ablated DMS-53 cells show a substantial decrease in lung tumor growth relative to controls. Correspondingly, we demonstrate increased tumor growth in mice harboring lung tumors formed by administration of DMS-53 or H1048 cells overexpressing DARPP-32 and t-DARPP proteins. Mechanistically, we describe how DARPP-32 isoforms promote SCLC growth through increased proliferation, Akt/Erk-mediated survival, and anti-apoptotic signaling. Taken together, we define new regulatory mechanisms of SCLC oncogenesis that suggest DARPP-32 isoforms may represent a negative prognostic indicator for SCLC and serve as a potential target for the development of new therapies. Citation Format: Sk. Kayum Alam, Li Wang, Yanan Ren, Christina E. Hernandez, Farhad Kosari, Anja C. Roden, Rendong Yang, Luke H. Hoeppner. New molecular mechanisms of small cell lung cancer growth [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5956.